Go to
http://www.modelflight.com.au/rc_model_electronics/hitec.htmscroll down to your servo, there is a link to the Hitech servo manual.
This gives the operating specs which show that all Hitech's servos expect a pulse between 3 and 5 volts at the rate of 50 per second.
Futaba for some reason are very shy about letting potential customers see their tech specs. Obviously their servos work, but there were rumours in the past that Futaba RXs only put out a 2.5 volt pulse, which might make things a bit marginal, but they should be compatible.
Usually, the only difference is the shape of different manufacturers plugs, which are often keyed to fit only their own RXs, but as modellers we have the means of removing the offending bit of plastic from the plug.